1. Field of the Invention
This invention is a mine borehole packer specifically designed for use with the water infusion process.
2. Description of the Prior Art
The water infusion process is a well known method used to control the movement of methane gas during mining operations in underground coal mines. Essentially it seeks to block the passage of the gas through the coalbed near the mine working face. It does this by first drilling a series of horizontal boreholes into the coalbed. Next in each borehole a hollow pipe is inserted. Then the pipe is packed between the pipe and the borehole i.e., the holes are prepared for infusion. And lastly water is pumped into and through the hollow pipe to exit from the far end thereof away from the working area. This water acts to prevent or block the flow of methane from the unmined part of the coalbed to the working face. The general object accomplished by this method is to keep the concentration of methane gas within the volume occupied by the miners and their equipment below one percent. Two United States Bureau of Mines publications describe this process in great detail and their contents are specifically incorporated by reference herein as background material. These publications are the Report of Investigations (RIs) entitled "Methane and Dust Control by Water Infusion" (RI 7640 published in 1972) and "Water Infusion of Coalbeds for Methane and Dust Control" (RI 8241 published in 1977).
The present invention is related to the step in the water infusion referred to above as the preparation for infusion. Previous packers commercially available for this purpose were constructed of metal and rubber with an overall length of about 5 feet. The ends were metal and the middle section (about 3.5 feet) an expansible rubber that acts to seal the borehole when inflated. Due to weight (each packer weights 45 lbs.) and manpower requirements, a typical 120 foot borehole would not contain these packers in a continuous abutting relationship. Normally many packers would be alternately joined by 5 feet pieces of metal pipes which results in less packers needed--e.g., twelve in the mentioned 120 feet borehole. One of the problems with this type of tradeoff is that only about 35 percent of the borehole is sealed by the 3.5 feet expandable middle sections. With less sealing of the borehole there is an increasing probability of water returning or short circuiting back along the borehole.
Several prior art patents are known which disclose grout filled packers used in boreholes. None employ the same structure as the present invention and are used for the same purpose. For example, the U.S. Pat. No. 1,630,470 to W. B. Clifford discloses an apparatus for breaking down ore bodies having a flexible envelope 25 of rubber which expands upon receiving a liquid via holes 36. The application of hydraulic pressure through bore 34 causes the envelope to contact the borehole with a high pressure area. Hence, the invention of Clifford is used to fracture the ore body by expanding a pressurized envelope while in the present invention the packer fluid is independent of the fluid in the mandrel and does not require a plug at end of the mandrel as in Clifford. These structural differences exist because the two inventions are used for different purposes--one to fracture the ore and one to act as a seal for a water infusion process.
Other U.S. patent references such as: No. 1,808,162 (Frantz); No. 3,918,522 (Suman); No. 2,634,113 (Joy); and No. 2,238,825 (Semler) disclose expandable structures, like packers, which could be inflated to fix various devices in boreholes. None relate to continuous inflatable packers used in water infusion processes.